Precision positioning stages, both linear and rotary, are used for laboratory and industrial applications including fiber optic and optical alignment systems.
Prior art technologies include means to achieve precision linear or rotational motion using either open-loop or closed-loop methodologies. In the context of right angle drives, of relevance are means that achieve precision motion while converting rotation along one axis into rotation along a second axis, orthogonal to the first. Application to linear output motion, concerns means of converting precise rotation about a first axis into precise translation along a second axis, orthogonal to the first. Various drive systems employed for stage motion include lead screws, recirculating ball screws, worm drives, gearboxes, and flexible shaft couplings. Prime mover actuation means include manual, electric stepper and servo motors, piezoelectric, magnetostrictive, and hydraulic. Subsidiary to these general design considerations, are supporting technologies relevant to the implementation disclosed herein, such as robust bearing designs, globoid worms, and motion encoders (.
Conventional precision motorized rotary stages exhibit a limited diameter clear aperture in comparison to the bearing footprint, with significant surrounding housing bulk, and a large motor assembly (protrusion) in proportion to the stage size (often conventional designs exhibit a motor housing larger than the stage.
What is needed is a compact mechanism that provides precision rotational drive to any size rotational stage with minimal customization; such a mechanism would not exhibit backlash. The problem for rotational stages is making a full line of standard and custom sizes without the prohibitive expense of new custom high precision parts for each variation. The use of such a mechanism to meet these objectives would be advantageous for driving linear stages, as well.
Globoid Worms
Worms are relevant to the present disclosure and more particularly, globoid worms, given features that can be specially adapted to address issues concerning precision motion drives. With respect to globoid worms, among the various names used to denote this type of gear are the following: globoid worm, hourglass worm, wormoid gear, double enveloping gear, enveloping worm, double enveloping worm, double throated worm, double globoid worm, and cone drive.
FIG. 1 depicts the different types of various prior art worms and associated worm wheels, absent depiction of the associated teeth; (a) cylindrical worm and cylindrical worm wheel, (b) cylindrical worm and enveloping worm wheel, (c) enveloping worm and cylindrical worm wheel, and (d) enveloping worm and enveloping worm wheel. The globoid (enveloping) worm is shown in FIGS. 1c and 1d. 
Advantages of the globoid worm over a traditional worm comprise increased driving efficiency (6-10% higher on 25:1 ratio) and increased loading capacity (about 30%). The most commonly cited disadvantages concerning conventional implementations of globoid worm drives include higher manufacturing cost and sensitivity of the enveloping pinion to the axial location. In order for the conventional device to be efficient (or turn at all), stage carrier backlash (moving platform relative to stage body) must be introduced. Due to the tooth geometry, the globoid worm can mesh not only with a mating enveloping gear but also with a correctly designed cylindrical helical gear. The substantial thickness of the mating gear is to exploit the heavy load advantage of the globoid worm drive.
There is need to exploit the advantages of the globoid worm for precision motion applications while overcoming the cited disadvantages.